The present invention is directed to a polymer make-down unit. More particularly, the invention is directed to an apparatus and method for flushing out piping and equipment that contains polymer emulsion.
Generally, a polymer (also known as a xe2x80x9cpolyelectrolytexe2x80x9d) is a chemical compound made up of repeating structural units which are comprised mainly of carbon and hydrogen. Each structural unit is referred to as a monomer, and by a process referred to as polymerization, the monomers are linked together to form long chains. Polymers typically carry an electrostatic charge, which, depending on the type of charge, attract particles which the polymer is exposed to and gives a polymer properties that make it suitable for specific industrial and manufacturing uses, as will be further discussed below.
The three types of electrostatic charge that a polymer may carry are positive, negative and no charge. When a polymer is comprised of positively charged units, e.g.xe2x80x94when it gets its charge from positively charged nitrogen atoms, the polymer is referred to as cationic. When a polymer is comprised of negatively charged units, e.g.xe2x80x94when it gets its charge from negatively charged oxygen atoms, the polymer is referred to as anionic. If the charge on the polymer is zero, e.g.xe2x80x94either because of an equal amount of positively and negatively charged units, or because of an absence of any charged units along its length, the polymer is referred to as nonionic.
There are many industrial and manufacturing processes in which polymers are used. For instance, polymers are commonly used in purification and flocculation processes by water treatment equipment to facilitate the separation of liquid and solid waste. In this case, the extremely large molecules of a polymer, having millions of charge sites, attract oppositely charged particles that are suspended in the water. Additionally, polymers are employed in chemical processing, coal preparation, painting, petroleum refining, plastics, petrochemicals, mining and mineral recovery, steel, textiles, phosphate and pulp and paper industries, as well as the previously mentioned water treatment and wastewater management systems and many other industrial and manufacturing processes. In these industries, polymers are typically employed to capture or recover, for further processing, particles or other solids which are produced as byproducts of the original industrial processes.
Polymers are typically available in either dry or liquid form, each of which has inherent advantages and disadvantages. One disadvantage of dry polymer is that it is required to be mixed with a large quantity of water in order to activate it (activation is discussed in detail below). The mixture of dry polymer with water can be problematic, as dry polymer typically does not readily mix with water, i.e.xe2x80x94agglomeration, characterized by unmixed pockets or bubbles of dry polymer, commonly occurs. Liquid polymer, on the other hand, is typically required to be mixed only with a small quantity of water, if any at all. Thus, liquid polymer has the advantage that it is premixed with a quantity of water that has been predetermined to insure optimal activation, or to which only a small quantity of water needs to be added to insure optimal activation. Additionally, liquid polymer is not subject to agglomeration since it has been premixed.
However, dry polymer has the advantage over liquid polymer of having a lighter shipping weight, which significantly reduces the cost to ship the polymer. Additionally, dry polymer has a longer storage shelf-life than liquid polymer and can be stored in inexpensive sacks as opposed to large drums and tanks.
Regardless of whether dry polymer or liquid polymer is employed, it is typically desired that polymer form a polymer emulsion prior to its use in a process. A polymer emulsion is a milk-like liquid mixture that is ideal for many polymer applications, and is formed by mixing unactivated polymer with water (the mixing process is also known as xe2x80x9cmake-downxe2x80x9d). In an unactivated state, the molecules of a polymer are typically in a coiled configuration. The coiled configuration of the molecules reduces the viscosity of the polymer and generally renders the polymer useless.
In order to be emulsified or activated, a sufficient amount of energy must be imparted to the mixture in addition to mixing the polymer with water. Energy is typically imparted to the mixture by vigorously agitating the mixture, such as by passing it through a pump or subjecting the mixture to blenders or beaters. This agitation causes the molecules of the polymer to uncoil in an extended chain-type arrangement. The exact amount of energy required for the activation of the polymer emulsion varies depending on the molecular weight of the polymer, the concentration of the solution, among other factors.
After being mixed with water, the polymer is typically aged in an aging tank, where any partially uncoiled polymer chains are permitted to completely uncoil and thus become fully activated. Since polymer is typically most useful when the polymer chains are completely uncoiled, it is common for the polymer to be activated in batches, each batch being permitted to age prior to its usage. When polymer has been fully activated, there is likely to be an increase in the viscosity of the polymer solution because of the full extension of the coil-like chain of molecules.
However, as is well known in the art, polymer that has been mixed with water and is partially activated eventually forms a gel-like substance when left in the piping and equipment of a polymer make-down system. Given sufficient time, the made-down polymer will even dry into a solid or plastic-like state. When this occurs in the piping and equipment of a polymer system, component fouling results. In order to avoid component fouling, polymer residue, which remains in piping and equipment after the polymer has been mixed and discharged from the system, must be removed from the piping and equipment. In a batch operation system, the piping and equipment of the system is subject to component fouling every time a batch is made.
Several patents disclose systems for mixing polymer and water to activate the polymer. For instance, U.S. Pat. No. 5,372,421 to Pardikes for a xe2x80x9cMethod of Inverting, Mixing and Activating Polymersxe2x80x9d disloses a method wherein polymer and a diluent are blended in a derated centrifugal pump and the polymer in the polymer/diluent mixture is relaxed by relaxing the system pressure. The relaxation of the pressure is accomplished by the use of a mixing pressure regulator, which causes polymer that passes through it to experience a sudden and abrupt pressure drop that facilitates the uncoiling of the polymer chain.
U.S. Pat. No. 5,407,975 to Pardikes for a xe2x80x9cDry Polymer and Electrolyte Mixing Systemxe2x80x9d disloses a funnel that has an inner wall along which water is swirled. Dry polymer is dropped into the vortex of the funnel to be wetted, and the wetted polymer is dropped through the spout of the funnel into the impeller of a pump. The pump transfers the mixure to a mixing vessel where a large volume of air is blown through the mixture so as to enhance its viscosity.
U.S. Pat. No. 4,778,280 to Brazelton for xe2x80x9cMixing Apparatusxe2x80x9d discloses a mixing apparatus having a first casings disposed above a second casing, but inverted in orientation. Dry polymer is guided by a funnel into water that is swirling tangentially within the first casing. A region of lower pressure is established at the discharge of the first casing by the swirling action, and causes the polymer and water to be drawn down into the second casing where it is vigorously mixed by the second casing""s impeller.
U.S. Pat. No. 5,338,779 to Brazelton for xe2x80x9cDry Polymer Activation Apparatus and Methodxe2x80x9d discloses an apparatus for activating a batch of dry polymer in dilution water. The apparatus includes a tank with dilution water, which is circulated at a high rate through a mixing assembly. The high rate of circulation through the mixing assembly causes a high shear flow condition, into which the polymer is dispersed to form a slurry. After dispersation and before hydration of the polymer, the rate of circulation through the mixing assembly is reduced to create a low shear flow condition, which permits the viscosity of the solution to increase.
However, none of the patents in the prior art, including the patents cited above, disclose a system or method in which the mixture of polymer and water is flushed from the piping and equipment so as to prevent component fouling.
Therefore, there exists a need for an apparatus and method for periodically and systematically flushing out polymer process piping and equipment.
The present invention, in accordance with one embodiment, is directed to a polymer make-down system having a mixing pump, a water source for providing a first quantity of water to piping at a suction end of the mixing pump, and a polymer source for providing a first quantity of polymer to piping at the suction end of the mixing pump. The system is configured so that, after the first quantities of water and polymer have been mixed, a second quantity of water is provided so as to flush the mixture of the first quantities of water and polymer from the system.
In accordance with another embodiment, the system is further provided with a polymer check valve between the polymer source and the suction end of the mixing pump. The polymer check valve is configured to prevent a flow of water to the polymer source. In accordance with still another embodiment, the system is further provided with recirculation piping coupled to piping at a discharge end of the mixing pump and to piping at an outlet end of the polymer check valve, such that the recirculation piping is configured to be flushed by the second quantity of water. In accordance with still another embodiment, the water source further comprises a water buffer tank configured to gravity feed the first and second quantities of water into the system. In accordance with still another embodiment, the system further comprises a flow meter for measuring the first quantity of water provided by the water source, and a water flow valve for adjusting a flow of the first quantity of water.